Field of the Invention
The present invention relates to a method of measuring the distribution of bending loss in the longitudinal direction of an optical fiber using a bidirectional OTDR measuring method, an optical line test method for detecting a failure position of bending loss using this measuring method, and a method of manufacturing an optical fiber having a small bending loss using this measuring method of bending loss distribution.
Background Art
As a technique of measuring the characteristics of the longitudinal distribution of an optical fiber, a technique referred to as a bidirectional OTDR measuring method is known (refer to IEICE Technical Report OSC2005-89 and ITU-Recommendations G. 650.1 (06/2004)).
A normal OTDR measuring method is a technique of acquiring backscattering optical waveforms (OTDR waveforms) in the longitudinal direction obtained from the time distribution of backscattering light of the pulse light that is incident from one end of an optical fiber, and obtaining information on a defect portion, a connection location, loss, and the like in the longitudinal direction of the optical fiber.
In the bidirectional OTDR measuring method, pulse light is entered from both ends of an optical fiber, and two OTDR waveforms are obtained from both ends bidirectionally.
Moreover, the distribution of a relative refractive index difference or a mode field diameter (hereinafter, refer to MFD) in the longitudinal direction of an optical fiber can be obtained by performing calculation processing of these two OTDR waveforms.
The bidirectional OTDR measuring method is a very useful tool in practice since characteristics distribution in the longitudinal direction of an optical fiber can be measured non-destructively.
Until now, in a method of measuring the longitudinal distribution of the optical properties of an optical fiber using the bidirectional OTDR measuring method, methods of measuring the relative refractive index difference, the MFD, a cut-off wavelength, and material dispersion are known.
However, a method of measuring the longitudinal distribution of bending loss that is one of the important optical properties of an optical fiber is not known.
On the other hand, for example, a method of carrying out a measuring method of bending loss described in IEC Standard Document IEC60793-1-47 Ed. 3 in a plurality of locations in the longitudinal direction of an optical fiber is considered.
However, in a location where this method is carried out, the optical fiber should be actually bent during the bending loss being measured.
For this reason, a problem occurs in that the locations where the bending loss can be measured is limited or the operation for obtaining the bending loss of a desired location becomes complicated.
In recent years, some bending loss insensitive fibers are proposed, and the importance of bending loss characteristics is increasing.
Accordingly, a technique capable of knowing bending loss characteristics distribution within an optical line or specifying a location having high bending loss within the optical line is desired.